In the prior art there has been a great need for apparatus that can measure the thickness of materials such as ice, wood, stone and concrete. For example, the armed forces have had need to measure the thickness of ice on streams and rivers in the winter to determine if they can drive trucks and even tanks across the ice.
Various techniques have been tried to measure the thickness of materials, but these techniques either have been bulky and expensive, they were inaccurate, or they did not work reliably.
Thus, there is a need for relatively inexpensive and simple apparatus that can measure the thickness of material such as ice, wood, stone and concrete.